Pneumatic system for a motor vehicle

ABSTRACT

The invention relates to a pneumatic system for a motor vehicle, said pneumatic system comprising a compressor unit, an accumulator unit and switch valves, via which the individual springs of the individual vehicle wheels are provided with pressurized air. A vent line is provided in the zone between the compressor unit and the switch valves. Said vent line opens into the atmosphere and can be blocked or released by a stop valve. The inventive system is further provided with devices that are used to limit the air mass flow discharged via the released vent line in certain intervals vis-à-vis an unlimited state in order to prevent undesired noises caused by the venting of the system. For example, a separately blockable high-pressure vent line can be connected parallel to a separately blockable main vent line, the free effective area of flow of the high-pressure vent line being smaller than that of the main vent line. Alternatively, a throttle element can be mounted in the vent line to limit the free effective area of flow of the vent line.

[0001] This invention relates to a pneumatic system for a motor vehicle with a compressor unit, a storage unit, as well as on-off valves via which the individual pneumatic springs of the individual vehicle wheels are supplied with compressed air; in the area between the compressor unit and the on-off valves, there is provided a vent line that can be locked or that can be released and that opens up into the atmosphere. As for the technical field, reference is merely made by way of example to DE 29 42 081 C2.

[0002] Pneumatic systems are distinguished from all mechanically buffered wheel suspension by greater flexibility or greater variability. In the case of two-axle pneumatic systems, for example, the height of the vehicle superstructure with respect to the ground and, thus, the ground clearance of the motor vehicle, can be altered. Usually, one employs so-called open pneumatic systems here where (in two-axle pneumatic systems), when the vehicle superstructure is lowered from a raised position, the air mass, that is to be evacuated for this purpose from the pneumatic springs, is evacuated by a so-called vent line and out into the atmosphere, that is to say, into the environment. If this lowering action is to take place within a relatively short time span, then the cross-section —more specifically, the clear through flow profile of the vent line that is usually provided in the vicinity of the compressor unit of the pneumatic system and that can be closed-off or cleared by means of a locking valve—must have a certain minimum size.

[0003] In this connection, reference is made expressly to the fact that the invention at hand is not confined to two-axle pneumatic systems but can also be used equally for single-axle pneumatic systems. It might furthermore be mentioned that the static air pressure—that [is located] upstream from the still closed on-off valves and that thus is applied in the pneumatic springs—can be within the order magnitude 4 to 10 bar; the dynamic pressure values can be definitely higher. The total system pressure also is usually higher, that is to say, up to the level of the pressure in a storage unit.

[0004] Along with a compressor unit—with whose help the system pressure, required for charging the mentioned pneumatic springs, or the pertinent required air mass will be supplied in the final analysis—there is also usually provided an already briefly mentioned storage unit in which are placed, for intermediate storage, air masses that are compressed by the compressor unit, because a reasonably dimensioned compressor would not be able to supply the air mass, needed for the desired lifting of the vehicle superstructure, within a justifiable time span. If the vehicle superstructure is then to be raised, then one can draw the necessary air mass, which is subjected to adequate system pressure, from the preferably completely filled storage unit.

[0005] This explanation clearly shows that the pressure, prevailing in the filled storage unit, must be greater than the pressure usually applied in the pneumatic springs because, otherwise, it would not be possible to fill those springs any further. By way of example, the pressure, prevailing in the filled storage unit, can be on the order of 15 bar. It is furthermore obvious that the compressor unit can be shut down after the complete filling of the storage unit, so long as no air mass is drawn from the latter [storage unit]. In this stage, it is desirable that one reduce the pressure applied in the pertinent line system, that is to say, in the line system between the compressor unit as well as the mentioned on-off valves, which, for instance, can be combined into a so-called valve block and on whose side—facing away from the compressor unit—the individual pneumatic springs are connected; in other words, one can aerate or vent this line system. A venting of this line system, that is to say, of the compressor unit, as well as the line segment between the compressor unit and the valve block or the on-off valves (naturally, without the storage unit that branches off from that line section and that can be closed off), is basically possible here via the previously mentioned venting line that is provided in the area between the compressor unit and the valve block.

[0006] But it was found that this aeration or venting or pressure release of the system—which initially is under the (higher) pressure of 15 bar, mentioned earlier by way of example—via this venting line is accompanied by an undesirable, practically no longer acceptable noise p generation. Abruptly, so to speak, m via this venting line, through which—in case of desired lowering of the vehicle superstructure, starting with a pressure level of 4-10 bar, for instance—only part of the air mass contained in the system is evacuated, whose [pressure level] is reduced compared to the higher pressure level of, for instance, 15 bar [sic]. Of course, a sound absorber or the like could be provided in the vent line; but that absorber represents a choke that works in an undesirable manner and that is always present, and, therefore, also in case the vehicle superstructure is lowered.

[0007] The object of the invention is to point out a comparatively more favorable expedient in helping to solve the problem complex just described. The solution of this problem is characterized by measures with whose help one can limit the air mass flow, emerging via the cleared vent line, during a certain time interval, as compared to an unlimited state. Advantageous embodiments and developments are covered in the subclaims.

[0008] According to the invention, the mass of the airflow, that is conducted through the vent line, can be limited, specifically, when the pressure in the system is to be reduced between the compressor unit and the valve block or the on-off valves, that is to say, after the storage unit has been completely filled. So that this—previously described—relatively high pressure will not be reduced abruptly (thus generating noises) via the vent line, it should be possible—for these cases—to limit the magnitude of the air mass that is moved through the vent line within a certain time interval, that is to say, the air mass flow. On the other hand, if the vehicle superstructure is lowered and if, accordingly, a part of the air mass, located in the pneumatic springs, is also evacuated via this vent line into the atmosphere, there should not be any such restriction or limitation, that is to say, in that case, the full flow cross section of the vent line should be available to facilitate the relatively fast lowering of the vehicle superstructure.

[0009] Basically, there are various possibilities of an optional restriction or a release, that is to say, lifting of this restriction or limitation of the air mass flow that can be conducted through the vent line within a certain time span. By way of example, using a switchable branch, one can optionally connect a sound absorber into the vent line although this solution requires relatively much structural space.

[0010] Comparatively more favorable measures are listed in the subclaims and will in the following be described in greater detail with reference to the enclosed FIGS. 1-3, showing the circuit diagrams of preferred exemplary embodiments of the invention at hand. The same elements are labeled with the same reference numbers in all figures.

[0011] Reference 1 is used to label the compressor unit of a pneumatic system of a motor vehicle that consists of an electric motor 1 a of a motor vehicle, a compressor 1 b, driven by electric motor 1 a, as well as a compressor 1 b, arranged in the pressure 1 c of said compressor, as well as a dryer 1 d, arranged in the compressor's pressure line 1 c. Air, suctioned in via a suction line 1 e, is condensed in compressor 1 b and is supplied—via pressure line 1 c, as well as an adjoining line segment 2—to a valve block 3, not illustrated in any further detail. From this valve 3—in which are combined individual on-off valves that are associated with the individual pneumatic springs and which are also labeled 3—this condensed air can be moved, in a controllable manner, into a storage unit 4 or directly into pneumatic springs, not shown, which are matched up with the wheels of the motor vehicle. As was explained earlier, valve block 3 or on-off valves 3—in case of a desired further filling of these pneumatic springs (in particular, for the purpose of lifting the vehicle superstructure)—are so switched here that, especially, the air mass, located in the filled storage unit 4, will be supplied to the pneumatic springs.

[0012] In case of a desired partial evacuation of the pneumatic springs (in particular, to lower the vehicle superstructure), the air, however, is not returned into the storage unit 4; instead, it is evacuated into the environment via a vent line 5. This vent line 5 is located here in the area of compressor unit 1, that is to say, vent line 5 here branches off from pressure line 1 c but it can just as well branch off from line segment 2. Naturally, a locking valve 6 is provided or required in the vent line 5 to ensure that air can get out of the system into the environment only when this is actually desired.

[0013] As indicated in the above explanations, this vent line 5 is used to evacuate air out of the system into the environment not only when a part of the air located in the pneumatic springs is to be taken out but also when, after the filling of storage unit 5, with valve block 3 being closed, the line segment 2 as well as compressor unit 1 are to be aerated.

[0014] In all exemplary embodiments, the locking valve 6, provided in vent line 5, is made as a pressure-controlled valve, that is to say, locking valve 6 can be opened by the system pressure prevailing between compressor unit 1 and valve block 3. For this purpose, a pilot control line 7 branches off from line segment 2; in that pilot control valve, a control valve 8 is provided, which is preferably made as an electromagnetic valve, and is placed against the control side of the locking valve 6. Accordingly, with control valve 8 being opened, locking valve 6 is basically opened or kept open until such time when the pressure in line segment 2 and in compressor unit 1 has dropped to the so-called threshold value of locking valve 6, for example, close to ambient pressure.

[0015] In the exemplary embodiment according to FIG. 1, there is parallel connected to the main vent line 5, which can be locked by means of locking valve 6, a high-pressure vent line 5′ that can also be locked separately by means of a so-called vent valve 9; the clear through flow cross section of that vent line 5′ is less than that of the main vent line 5. This vent line 5′ here branches off from the pilot control line 7, upstream from the control valve 8, but it can just as well also branch off directly from line segment 2. The just mentioned clear through flow cross section of the two vent lines 5, 5′ in the process is determined in each case by a narrowest cross section, that is to say, by so-called “narrow” in these vent lines. Most of the time, the clear through flow cross section of the particular valve, provided in vent line 5 or 5′ (locking valve 6 or vent valve 9), defines this clear through flow cross section. If a part of the air mass is to be taken out of the pneumatic springs (not shown), then this part, as usual, with valve box 3 suitably switched, is conducted via line segment 2 into vent line 5 as well as into pilot control line 7 so that, with vent valve 9 being closed, locking valve 6 is opened as a result of the opening of control valve 8 and this air mas can then be released into the environment via the vent line 5. Relatively fast air evacuation is desired; therefore, vent line 5 or the open locking valve 6 has an accordingly large clear flow cross section.

[0016] If, on the other hand, with valve block 3 being locked, that is to say, closed, after the filling of storage unit 4, line segment 2 as well as compressor unit 1 are to be aerated, then, as described earlier, control valve 8 remains closed. On the other hand, vent valve 9 is then opened so that the air mass, located in the mentioned line segment 2, and placed under over pressure when compared to the atmosphere, can then get into the environment via the cleared high-pressure vent line 5′. The clear through flow cross section of this vent line 5′—that is preferably defined by the clear cross section of the opened vent valve—is made so small here that this pressure reduction, starting from a high pressure level (that is to say, the previously mentioned figure of 15 bar, given by way of example) will be delayed and that, therefore, it will not be accompanied by any undesirable noise generation.

[0017] The air mass, that is to be evacuated in case of a venting of line segment 2 as well as compressor unit 1, is mostly considerably smaller than the air mass that must be evacuated into the environment, out of the pneumatic springs, in case the vehicle superstructure is lowered. The clear through flow cross section of the high-pressure vent line 5′ is considerably smaller than the pressure in the main vent line 5; nevertheless, line segment 2 is therefore vented via this, so to speak choked high-pressure vent line 5′ within a justifiably short span of time. As for the rest, after expiration of a small span of time, after the absolute pressure peak values have already been reduced, vent valve 9 can be closed and control valve 8 can be opened so that the continued residual venting will take place via main vent line 5. There is therefore no reason to fear any annoying noise generation on account of the fact that pressure reduction has already taken place.

[0018] In the exemplary embodiment according to FIG. 2, a choke element 10 is provided in the only vent line 5; with the help of that choke element, the clear through flow cross section of vent line 5—that has been cleared by opening the locking valve—can be limited. Basically, this choke element 10 can be suitably adjusted by an adjusting device, not shown, that is to say, in case of a desired lowering of the vehicle superstructure and an attendant air mass evacuation out of the pneumatic springs, via vent line 5, the free through flow cross section of that vent line can be maximized, that is to say, the choke effect of the variable choke element 10 is minimized. On the other hand, in case of a desired venting of line segment 2, as well as compressor unit 1, with valve block 3 being locked, the choke effect of choke element 10 is maximized in order to minimize the free through flow cross section of vent line 5. This measure likewise thus makes it possible to prevent the undesirable noise generation, in the last-mentioned operating state, that was described initially.

[0019] By way of an advantageous development, choke unit 10 can be so designed that it will automatically and variably limit the free through flow cross section of vent line 5 as a function of the pressure level prevailing upstream from choke element 10. The adjusting device, mentioned in the preceding paragraph, will then not be needed. With the application of a high pressure in case of desired venting of the system (on the order of magnitude of 15 bar, as mentioned by way of example earlier), a free through flow cross section of vent line 5 is thus limited by itself, that is to say, automatically, whereas, at a lower pressure (for example, on the order of magnitude 9 bar), the maximum possible passage cross section is released because of undesirable noise generation does not occur then anyway.

[0020] No design embodiments are given in FIG. 2 for the two described variants of the variable choke element 10 because such variable choke elements are known or can be shaped in a relatively simple fashion. A variable choke element, that is adjusted automatically as desired, for example, can have a slide that more or less restricts the free through flow cross section of vent line 5 and that, on the one hand, is spring-loaded and, on the other hand, has a control surface that is impacted by pressure upstream from the choke element 10. If there are high pressure values upstream from choke element 10, then this slide is moved by the pressure, acting upon said control surface, against the force of the spring element, into a position that relatively greatly limits the free through flow cross section, whereas, on the other hand, in case of low pressure values, upstream from choke element 10, this slide is moved, by the force of the spring element, into a position that practically does not have a choking effect, that is to say, that more or less completely releases the through flow cross section of vent line 5.

[0021] Only a single vent line 5 is also shown in the exemplary embodiment according to FIG. 3. In contrast to the previously mentioned exemplary embodiments, it is essential for the operation of this exemplary embodiment that the locking valve 6, provided in vent line 5, be opened by the system pressure prevailing in the area of the compressor unit and applied via the previously mentioned pilot control line 7. A so-called pressure release volume 11 is provided upstream from locking valve 6 and downstream from control valve 8 in or on pilot control line 5. One embodiment is illustrated specifically here; in this embodiment, the pressure release volume 11 is located directly in the pilot control line 7; in an alternate embodiment, this pressure release volume 11 can branch off from pilot control line 7 via a tap line (not shown).

[0022] This exemplary embodiment, according to FIG. 3, works in the following manner. It was mentioned earlier that, in case of a venting of line segment 2, as well as compressor unit 1, the air mass that is to be evacuated will be considerably less than the air mass that must be evacuated out of the pneumatic springs into the environment, in case the vehicle superstructure is lowered. If, in other words, there is a venting of line segment 2—as mentioned earlier, starting with a relatively high pressure level, for example, on the order of magnitude of 15 bar—then, after the opening of control valve 8, this air mass, which is under high pressure, expands into the pressure release volume 11 that is considerably larger when compared to the volume of the island control line 7. Before the pressure-controlled locking valve 6 can thus be opened at all there takes place, via pressure release volume 11, already such a pressure reduction (for example, down to the level of 4-10 bar which is customary when the vehicle superstructure is lowered), that, after the opening of locking valve 6, there can no longer be any of the noise generation that was mentioned initially and that can be prevented with the help of the invention at hand. Here again, on account of the pressure reduction in the pressure release volume, the air mass flow, straining through the cleared vent line 5, following the opening of locking valve 6, is limited.

[0023] This pressure release volume 11 practically exerts no influence in case of a desired lowering of the vehicle superstructure because the air mass, which is then to be evacuated via vent line 5, is so great that its minor partial pressure release in pressure release volume 11 can be neglected. This exemplary embodiment, according to FIG. 3, is thus distinguished by a particularly simple structure; it must also be pointed out that, naturally, a plurality of details can certainly be designed so as to deviate from the explained exemplary embodiments, without going beyond the content of the claims.

List of References

[0024] 1 compressor unit

[0025] 1a electric motor

[0026] 1b compressor

[0027] 1c pressure line

[0028] 1d dryer

[0029] 2 line segment

[0030] 3 valve block/on-off valve or valves

[0031] 4 storage unit

[0032] 5 (main) vent line

[0033] 5′ high-pressure vent line

[0034] 6 locking valve

[0035] 7 pilot control line

[0036] 8 control valve

[0037] 9 vent valve

[0038] 10 choke element

[0039] 11 pressure release volume 

1. Pneumatic system for a motor vehicle with a compressor unit (1), a storage unit (4), as well as on-off valves (3), via which the individual pneumatic springs of the individual vehicle wheels are supplied with compressed air, where, between compressor unit (1) and on-off valves (3), there is provided a vent line (5) that opens up into the atmosphere and that can be locked by a locking valve (6) or that can be cleared, characterized by measure with whose help one can limit the air mass flow, emerging via the cleared vent line (5), during a certain time interval, with respect to an unlimited state.
 2. Pneumatic spring system according to claim 1, characterized in that, connected parallel to a separately lockable main vented line (5), there is a separately lockable high-pressure vent line (5′) whose clear through flow cross section is smaller than that of the main vent line (5).
 3. Pneumatic spring system according to claim 1, characterized in that in vent (5), there is provided a choke element (10) with whose help one can limit the free through flow cross section of vent line (5).
 4. Pneumatic spring system according to claim 3, characterized in that the choke element (10) automatically and variably limits the free through flow cross section of vent line (5), as a function of the pressure level prevailing upstream from choke element (10).
 5. Pneumatic spring system according to claim 1, where the locking valve (6), provided in vent line (5), is opened by the system pressure that prevails between the compressor unit (1) and on-off valves (3) and that is applied via a pilot control line (7), characterized in that a pressure release volume (11) is provided between locking valve (6) and a All control valve (8), in or on pilot control line (7). 